In past years it was common to mount a rotary switch on a transmission housing externally thereof to receive mechanical gear selection inputs from the operator of a vehicle through various linkages and output gear selections to appropriate output means such as a decoder module and the transmission electronic control unit via electronic signals. The switch includes a quadrant with a selected number of electrical switch segments disposed thereon with each segment providing an output to the output means. A manual valve controlling hydraulic operation of the transmission is mechanically coupled to a plate having indexing detents, called a detent lever, mounted on a shaft and pivotably movable therewith. The shaft extends through the transmission housing wall and a switch bar is fixedly attached to the shaft externally of the transmission housing so that when a vehicle operator selects a gear the switch bar within the rotary switch moves across the quadrant to a predetermined position to engage one or more of the electrical segments. In certain systems the electronic control monitors the gear position along with other inputs, for example, throttle position, output shaft speed, engine speed, engine load and so on.
In U.S. Pat. No. 5,736,701, assigned to the assignee of the present invention, a switch system is disclosed which is mounted within the transmission housing in order to avoid placing the switches in a hostile environment subject to water splash and the like as well as to avoid tolerance stack-up problems associated with linkages employed when mounting the switches externally of the transmission housing.
In the referenced patent, a movable electrically conductive contact assembly is mounted directly on a first face surface of the detent lever of the manual valve assembly. A generally flat quadrant shaped housing member, formed of electrically insulative material, is rotatably mounted on the manual shaft in a position adjacent to and overlying the detent lever. A stationary, electrically conductive contact assembly is disposed on a face of the housing member overlying the first face surface of the detent lever. A plurality of generally L-shaped attachment projections, extending from the outer periphery of the housing member, have legs spaced from the face of the housing member extending toward the manual shaft receiving bore so that the legs extend over at least a portion of the opposite, second face surface of the detent lever. A generally L-shaped locking projection, extending from the housing, is received through a cut-out portion of the detent lever when the attachment projections are out of alignment with the detent lever. Following insertion of the locking projection through the cut-out portion, rotation of the housing relative to the detent lever causes a leg of the locking projection to move over at least a portion of the second face surface of the detent lever when the attachment projections are aligned with the detent lever. The housing member is provided with a pair of prongs which receive therebetween the roller of a roller/spring assembly to thereby maintain the housing member in a selected X-Y position. The distance between the legs of the attachment and locking projections from the face surface of the housing member determines the position of the housing member in the Z direction in cooperation with a spring bias provided by the movable contact assembly. The stationary contact assembly has a plurality of arc-shaped contact segments separated from one another in a radial direction by rib members which extend from the surface of the housing a selected distance beyond the contact segments to thereby prevent short circuiting between adjacent contact segments by debris or the like.
Switch systems made in accordance with the '701 patent are very effective in obviating the prior art hostile environment and stack-up problems; however, in the transmission of certain vehicles the space available to place a switch system within the transmission housing, particularly in the direction taken along the longitudinal axis of the manual shaft, i.e., in a vertical or Z direction, is insufficient for housing structure of the switch system to extend beyond the second face surface of the detent lever in the vicinity of the arcuate stationary contacts, that is, L-shaped attachment projection 24a and leg 24d of the patent. The legs of attachment projections 24a, 24b, 24c and locking projection 24g are used to maintain an appropriate gap, that is, they are used in determining the position of the stationary contact assembly relative to the detent lever and, concomitantly, movable contact elements mounted on the detent lever for electrical engagement with respective stationary contacts. Leg 24d of abutment 24a supports the movable contact assembly the most during the index positions of DRIVE and LOW. In order to operate as intended, it is imperative that continuous engagement be maintained between the movable electrical contacts on the detent lever with the stationary electrical contact assembly.
The problem of ensuring this maintenance of engagement is exacerbated by the fact that the switch system housing, molded of electrically insulative material, typically is subject to some degree of warpage.